Tiling on upstairs floor

BarraOG

I wish to renovate an upstairs bathroom. The floor is 18mm plywood. I can easily establish where the joists are under it if necessary. I will be dividing the room into two parts by building a stud wall. The smaller part will be used for storage. I've included pictures of the room and floor. Should I add another layer before tiling? What would you recommend? The door is already hung for the room but I have a brother who is a carpenter so I can get him to trim the bottom of it. The gap from the floor to the door is around 25mm at the moment. The floor has only ever had lino on it. I'll place the shower with raised tray where I patched the door that led into the attic and mount a sink on the stud wall. I'll get a plumber to do the pipe work. Do I need special adhesive? My dad is really good at tiling so he will be helping me.

Citizen Six

If your dad is really good at tiling, then why doesn't he know what to do?

BarraOG

He isnt a professional tiler but has tiled lots of bathrooms and kitchens for extended family over the years. The floors he has tiled have been on concrete so he wasn’t sure if I’d need to do anything special in this case.

greasepalm

Do you not have to seal the floor and slightly up the wall to make it a wet room.

This was done for my upstairs bathroom and shower tray. + have a tiled floor.

I regretted getting a shower tray as its gone out of shape and would have gotten it tiled if i thought about it + it has glass screens to keep the water in that area.

Larbre34

18mm ply is about as sturdy as a joisted floor gets, but for a belt and braces approach I'd lay 6mm cement based backer boards, you'll have a surface as good as any poured floor. Then your Pop can carry on with his favourite adhesive as normal.

BarraOG

https://www.boards.ie/discussion/comment/120262562#Comment_120262562

I want to keep this very simple. The old bathroom was a disaster with a cheap door leading into the attic. I plan to have a raised shower tray and a standard enclosure sat on the tiled floor. So I’m not planning to do a wet room.

greasepalm

But if floor is not sealed and you get a leak where does water go ?

10-10-20

Not a tiler but... you definitely do not have half-enough screws in the existing 18mm ply, plus you have enough cuts already in it (nevermind the joint directly under the shitter - spot-loading!) to make me think that you should overlay it with 6mm or 9mm ply or backer/cement board with offset joints, just to stiffen it more.

Dr_Colossus

+1 to what Labre34 and 10-10-20 said above. Not a tiler either but a lot of pros you can't trust so if you want a job done well do it yourself or in this case your dad. When I did my ensuite I had to replace the existing floor due to rot caused by previous tiler, installed plenty of noggins to solidify the floor as much as possible then laid 18mm OSB followed by 6mm magnesium board which was both set and screwed to existing floor every 6" and thereafter the floor was tanked.

As mentioned if you can take up any of the existing floor (looks like sections of it have been up previously) put plenty of noggins underneath and then screw it down well. Magnesium board I found good for the floor as it's very solid/rigid even at 6mm. I used 12.5mm cement board for the walls around the shower but others favour foam board which I don't fully trust as there's quite a bit of give in it. Cement board is not waterproof so it or plasterboard as in your case needs to be well tanked especially around the shower.

astrofool

Lots and lots of screws of a good length (ensuring not to go through existing pipes and wires underneath, check with a builder, but every 6-8cm would be a good idea). Cement board and tanking kit would be recommended as well.

mick121

That Ply floor is in to many pieces and each section could move independently leading to cracks in the tiles.More screws into the joists about every 6 inches.

I'd fix 6mm cement board over it, keep the boards as big as possible to reduce joints.Screw every 6inches using galvanized/plasterboard screws with appropriate washers that won't rust over time

GreeBo

take up the existing floor and then go with 9mm ply and 6mm cement or magnesium and then you dont have to worry about levels.

the existing flooring is doing little for support, its just in your way.

BarraOG

Thanks for all the replies! How is cement board attached to plywood, screwed or adhesive? Can you walk on this board before tiling it? Is it tough in other words?

mick121

Screwed down with washers, they must be galvanized etc to prevent rust.Make sure the screws are not too long incase there are pipes near the underneath of the existing floor.You can stand/walk on cement board once it's on the floor.

e.r

Glue & screw the backer board.

as another poster said, take up existing.

then use 12mm osb & 12 cement board ( glue and screw this layer)

any standard flexible adhesive should do the job

josip

We've a small bathroom and covered the floor with 2 pieces of 18mm ply. Used a shedload of screws to have it rock solid before tiling on top of it. But 3 months later the grout started to crack and work out. Got it regrouted with flexible grout but the same happened after 3 months. No cracks in tiles thankfully, but the grout is unsightly. So defo go with what the posters above are recommending.

GreeBo

plywood & screws are only as good as the framing underneath.

When you say 2 pieces, do you mean 2 layers or just 2 distinct sheets?

If its not layers, were the cracks near where the joint is?

irishbuzz

Not cheap but Schluter Ditra underlayment is for this type of purpose.

josip

https://www.boards.ie/discussion/comment/120325571#Comment_120325571

1 layer of ply in 2 pieces on top of floor boards. The floor boards would have been well screwed in to the joists also. DIY job, but both builder and tiler told me it would be ok. No cracks in tiles, just the grout. Ah, the benefit of hindsight :(

10-10-20

https://www.boards.ie/discussion/comment/120329693#Comment_120329693

Ditra will give some protection from the sheering movement or lateral forces (differential movement stresses) on the underlying substrate, but it cannot protect against flexing which is due to compressive loads as these will cause the tiles to see-saw and crack the grout and eventually work themselves loose. The backing/substrate still needs to be rock-solid to work properly. Ditra does improve matters all of the same, but isn't a fix for all.

GreeBo

https://www.boards.ie/discussion/comment/120329741#Comment_120329741

did it crack everywhere or just where the ply joint was though?

BarraOG

Still havent got a chance to start this. A number of you mentioned taking up the ply floor and laying a new one. The problem is that the studded walls are sitting on the floor. The floor is surrounded on three sides by attic space so the ply floor stops under the stud. Maybe I should try and prop up the stud wall and get a new floor in under it or maybe that’s madness. The room is shown in the picture in my first post above and I will be adding a stud myself to reduce the size of the room and make a corner for the shower.

mick121

Just put cement board over it if you can.Screw every 4 inches with galvanized screws and washers.